I am using NSURLSessionDownloadTask with background sessions to achieve all my REST requests. This way I can use the same code without have to think about my application being in background or in foreground.
My back-end has been dead for a while, and I have taken that opportunity to test how does NSURLSession behave with timeouts.
To my utter surprise, none of my NSURLSessionTaskDelegate callbacks ever gets called. Whatever timeout I set on the NSURLRequest or on the NSURLSessionConfiguration, I never get any callback from iOS telling me that the request did finish with timeout.
That is, when I start a NSURLSessionDownloadTask on a background session. Same behavior happens the application is in background or foreground.
Sample code:
- (void)launchDownloadTaskOnBackgroundSession {
NSString *sessionIdentifier = @"com.mydomain.myapp.mySessionIdentifier";
NSURLSessionConfiguration *backgroundSessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfiguration:sessionIdentifier];
backgroundSessionConfiguration.requestCachePolicy = NSURLRequestReloadIgnoringCacheData;
backgroundSessionConfiguration.timeoutIntervalForRequest = 40;
backgroundSessionConfiguration.timeoutIntervalForResource = 65;
NSURLSession *backgroundSession = [NSURLSession sessionWithConfiguration:backgroundSessionConfiguration delegate:self delegateQueue:[NSOperationQueue mainQueue]];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://www.timeout.com/"]];
request.timeoutInterval = 30;
NSURLSessionDownloadTask *task = [backgroundSession downloadTaskWithRequest:request];
[task resume];
}
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
NSLog(@"URLSession:task:didCompleteWithError: id=%d, error=%@", task.taskIdentifier, error);
}
However, when I use the default session, then I do get an error callback after 30seconds (the timeout that I set at request level).
Sample code:
- (void)launchDownloadTaskOnDefaultSession {
NSURLSessionConfiguration *defaultSessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
defaultSessionConfiguration.requestCachePolicy = NSURLRequestReloadIgnoringCacheData;
defaultSessionConfiguration.timeoutIntervalForRequest = 40;
defaultSessionConfiguration.timeoutIntervalForResource = 65;
NSURLSession *defaultSession = [NSURLSession sessionWithConfiguration:defaultSessionConfiguration delegate:self delegateQueue:[NSOperationQueue mainQueue]];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://www.timeout.com/"]];
request.timeoutInterval = 30;
NSURLSessionDownloadTask *task = [defaultSession downloadTaskWithRequest:request];
[task resume];
}
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
NSLog(@"URLSession:task:didCompleteWithError: id=%d, error=%@", task.taskIdentifier, error);
}
I cannot seem to find in the documentation anything that suggests that the timeout should behave differently when using background sessions.
Has anyone bumped into that issue as well? Is that a bug or a feature?
I am considering creating a bug report, but I usually get feedback much faster on SO (a few minutes) than on the bug reporter (six months).
Regards,